Changing button labels

[ Moderator note: moved to Fixing WordPress. Please do not use Developoing with WordPress for these topics. ]

Hi

I am looking for a way to change “HOME, …, “”SIGN IN”, “JOIN US” header buttons’ labels. It does not matter whether to change it by changing a theme settings/files or installing a separate plugin. I searched thoroughly the source files of the installed theme and source files of WordPress itself but did not find a place where I can do it.

Thanks in advance!